1. Field of the Invention
The present invention relates to an easy-open container, a manufacturing method thereof and a manufacturing device thereof.
2. Description of Related Art
For packaging foods and the like, there have been widely used a lidded container including a container body with a flange extending from a circumference of an opening of the container body and a filmy lid, the container being hermetically sealed, after filling the container with the foods and the like, by heat-sealing the flange of the container body and the lid.
Such lidded container requires a high sealing performance in terms of securely preserving the foods and the like contained therein, where the flange provided to the container body and the lid are heat-sealed so that a seal part formed by the heat-sealing becomes difficult to be peeled off, while the container requires an easy-open performance in terms of usability in opening the lid so that the lid can be easily peeled off from the container body. Accordingly, the lidded container requires to have the sealing performance and the easy-open performance as contradictory characteristics at the same time.
However, since leakage of contents is a fatal problem for the lidded container (easy-open container) having the characteristics described above, a sealing condition (sealing temperature and sealing pressure) is set to high at the expense of the easy-open performance to some extent so that the seal part becomes difficult to be peeled off to prevent the contents from leaking out from the container, which has resulted in losing the easy-open performance of the container.
With such background, arts for obtaining an easy-open container having both the high sealing performance and the easy-open performance have been studied from various quarters. For instance, there has been proposed an art in which a container that is opened by peeling a seal layer of a container body from a layer adjacent to the seal layer, and a notch is provided on a flange of the container body so that the seal layer can be properly cut off from the container body by peeling the seal layer along the notch (see, for instance, Reference 1: JP-A-63-78). There has been proposed another art in which a container and a lid are heat-sealed with a projected sealing board to form gathered resin parts respectively on both boundaries between a seal part and non-seal parts (see, for instance, Reference 2: JP-A-2-67125). There has been proposed still another art in which an opening surface is provided between a seal layer and a layer below the seal layer of a container and a gathered resin part is formed only on an inner boundary between a seal part and a non-seal part (see, for instance, Reference 3: JP-A-2-233378).
However, in the art disclosed in Reference 1, notch forming on the flange of the container body and positional adjustment in sealing are difficult, resulting in poor workability and high production cost.
In the art disclosed in Reference 2, when the gathered resin parts are formed on both boundaries, even in a case where one of the gathered resin parts is crushed by heat-sealing in another step, a part of the gathered resin part formed on an outer circumferential part of a bar is stretched when the lid is opened, resulting in poor opening appearance. In addition, even when the opening surface is provided between a seal layer and an adjacent layer adjacent to the seal layer of the container, the seal layer is not stably cut off, resulting in poor opening appearance.
In the art disclosed in Reference 3, a sufficient easy-opening performance cannot be realized in actual use, where the seal layer of the container at an open trigger of the container is not cut off or not peeled off from the layer below the seal layer, and further, when a stress is applied to open the container, a surface layer is stretched, which causes poor opening appearance. In addition, the easy-open container having the above arrangement causes difficulty in starting opening.